The present invention relates to apparatus comprising an ion mobility spectrometer, a mass spectrometer, a method of ion mobility spectrometry and a method of mass spectrometry.
Ion mobility spectrometers (“IMS”) are known which are provided at sub-ambient pressure conditions within the vacuum chamber of a mass spectrometer. Typically, the chamber housing the ion mobility spectrometer is maintained at a gas pressure in the range of 0.1 to 10 mbar. The chamber housing the ion mobility spectrometer must be provided in a differentially pumped vacuum chamber in order to minimise gas loading of a mass analyser which is arranged downstream of the ion mobility spectrometer in a separate vacuum chamber. Depending upon the location of the ion mobility spectrometer in the overall mass spectrometer, ions may have passed through a region of relatively low pressure prior to entry into the chamber housing the ion mobility spectrometer. If ions pass through a region of relatively low pressure immediately prior to the chamber housing the ion mobility spectrometer then it is necessary to drive the ions into the chamber housing the ion mobility spectrometer against a significant outflow of gas from the chamber. The requirement to drive ions into the chamber housing the ion mobility spectrometer against a significant outflow of gas can be particularly problematic especially if some of the ions are relatively fragile or have relatively low mobilities since the use of a relatively high electric field to drive the ions into the relatively high pressure chamber can lead to undesired effects such as ion fragmentation and/or ion mobility effects.
It is therefore desired to provide an improved apparatus comprising an ion mobility spectrometer.